Composite shafts for use in torque carrying, power transmission applications are highly dynamic as in motor propshafts, marine shafts, aircraft flap shafts, helicopter drive shafts, industrial drive shafts, wind turbines and dynamometers. They are required to have good torsional, static and fatigue strength coupled with a high whirling resistance. To achieve the latter, low shaft densities, large diameters, reduced length and high longitudinal modulus are all advantageous characteristics. However, for any specific design application the lengths and diameters of the shafts are fixed. A material combination with high specific axial modulus (high longitudinal modulus and low density) is required to produce a shaft with high resistance to whirling. To achieve this, composite tubes reinforced with high modulus fibres and in particular high modulus carbon fibre reinforced plastics (CFRP) are the materials of choice. Torque is transferred through flanged end fittings attached to the shaft ends. A structurally efficient design of this joint mechanism is the subject of this invention.
Fiber reinforced composite shafts exhibit advantages over metallic shafts, i.e., they are lighter in weight, more resistant to corrosion, stronger, and more inert. Fibre reinforced drive shafts comprising both glass fibers and carbon fibers in a resinous matrix have been disclosed in U.S. Pat. No. 4,089,190, “Carbon Fiber Drive Shaft” by Worgan and Reginald. Tubular fibre reinforced composites have been proposed, as demonstrated by U.S. Pat. No. 2,882,072 issued to Noland on Apr. 14, 1959, and U.S. Pat. No. 3,661,670 issued to Pierpont on May 9, 1972, and in British Pat. No. 1,356,393 issued on Jun. 12, 1974. Vehicle drive shafts from tubular fiber reinforced composites, as demonstrated by U.S. Pat. No. 4,041,599 issued to Smith on Aug. 16, 1977, and to Rezin and Yates (Celanese Corporation) in U.S. Pat. No. 4,171,626. Here the filaments bearing an uncured thermosetting resin are wound around a mandrel until the desired thickness has been established, whereupon the resinous material is cured. Zones or layers are positioned circumferentially within the wall of the shaft in the specific angular relationships there disclosed. The transmission of torque into the composite shaft through mechanical and adhesive joints is the subject of a series of further Celanese U.S. patents granted in 1980-1981: U.S. Pat. Nos. 4,185,472, 4,187,135, 4,214,932, 4,236,386, 4,238,539, 4,238,540, 4,259,382 and 4,265,951. Mechanical fixing of a tubular composite shaft through an internally fitted tubular metallic splined interface is described in JP2001065538 by Manabu et al (Mitsubishi Motors Corp.)
Composite shafts can be manufactured in a variety of ways. Filament winding allows combinations of winding helix angles, ply thicknesses and fibre type to be used in optimised lay ups. The main shaft may be made from fibrous reinforcement in a polymeric matrix. The fibres may be based on carbon, glass, ceramic or high stiffness polymer filaments or from hybrid mixes of these fibrous forms. The matrix may be based on thermosetting polymers such as epoxy or for high temperature applications polyimide or bismaleimides. Production methods can be based on laying combinations of low angle helical, higher angle, helical and hoop oriented layers distributed throughout the tube thickness to give combinations of controlled wall section, torsional and longitudinal stiffness and strengths commensurate with the design requirements. The composite tube properties are tailorable through control of the relative thickness of the plies and angles relative to the axis of the shaft. Fibres wound at low angles <30° impart high axial tensile properties; fibres wound at 40-50° impart high torsional properties; fibres wound at 75-89° impart high hoop properties.